There is known an eccentrically oscillating speed reducer of a background art including a plurality of crankshafts, a cylindrical gear for transmitting a power inputted to one crankshaft of the plurality of crankshafts to remaining crankshafts, and a pair of rolling bearings supporting the cylindrical gear (refer to, for example, Patent Reference 1). Patent Reference 1: JP-A-9-57678 (pages 3, 4, FIGS. 1, 3)